The present invention relates to the field of coating of articles, especially medical products and/or medical devices.
The application of biocompatible, lubricious coatings to medical devices is well known and widely practiced. Examples of patents discussing the coating of such devices include U.S. Pat. Nos. 4,801,475, 5,023,114, and 5,037,677, the disclosures of which are hereby incorporated by reference herein.
Whether the coating is applied by dipping, spraying, or other means, the surface is normally coated with a continuous film, i.e. without "skipping" areas.
The coatings described above may be temporary hydrogels, less fugitive polymers of N-vinylpyrrolidone, or firmly attached and abrasion-resistant products such as those known commercially by the trademark HYDAK with grafted mucopolysaccharide surfaces. The HYDAK product is available from Biocoat Incorporated, of Fort Washington, Pa. HYDAK is a registered trademark of Biocoat Incorporated.
The preferred method of applying such coatings is withdrawal from a dipping bath at controlled speeds, the coating thickness so produced being a consequence of the withdrawal speed, the viscosity of the material being applied, and other factors. The overall result is a desirably uniform, continuous, and durable coated surface.
However, with certain devices, such as a balloon catheter that is intended to aid in the placement of stents in the vascular system, it is highly desirable that most of the length of the catheter be coated with a non-thrombogenic, slippery material, while the balloon(s) should not be slippery. The reason for coating the catheter body but not the balloon is that if the balloon surface is also slippery, the stent riding on it may slip out of place prematurely before it is properly placed. On some such interventional catheters, there may even be two or more balloons on the same catheter, spaced apart on a multilumined catheter shaft. On a sixty-inch catheter, two or more balloons may be located near the distal end and spaced only a short distance apart.
The primary purpose of the multiple-balloon arrangement is to enable the radiologist to carry out more than one diagnostic or remedial function without having to perform catheter insertions more than once. Thus, the foremost advancing balloon might be employed to expand the blood vessel in the area of constriction. A lubricious, hydrophilic surface on this balloon is usually highly desirable. The second balloon may be carrying a stent to be placed in the expanded area of the blood vessel to retard or prevent re-stenosis. The surface of the second balloon should hold the stent securely until the point of deposit is reached. The surface of this second balloon, which is called the "transport balloon", should not be slippery.
The dipping process for coating catheters and guide wires does not provide any obvious means of accomplishing the selective coating of different sections of the device. Normally, the length of the device to be coated is immersed in the coating bath and then withdrawn at a carefully controlled rate, so that the entire length is uniformly covered with a film of the desired thickness. In this process, there is no way of discontinuing the deposition precisely when the edge of the transport balloon is reached, and of resuming the deposition precisely when its trailing edge has passed.
The above-described problem might be solved by choosing some other method of applying the coating than dipping, but the alternatives have their own problems. Spray coating, for example, is labor-intensive, and expensive to apply to individual catheters, and in addition is capable of painting the precise margins at the leading and trailing edges of the transport balloon only when applied by an artist with special "spray pens". Another solution is to fabricate and attach the transport balloon after the remainder of the catheter has been coated. But the latter process has the disadvantage that coating of the catheter tends to plug the air port from the lumen at the site of the balloon to be mounted later. There are still other alternatives that could be devised, but each has its own negative features.
The above-described problem is not limited to catheters, but is encountered with other medical devices, as will be described later.
The present invention provides a method which solves the above problem in an economical, practical, and effective way. The present invention provides a method for selective coating of a wide variety of medical products and devices. The invention can also be used to coat other articles where selective coating is desirable.